1. Field of the Invention
The present invention relates to two-dimensional bar codes. More specifically, the invention relates to a matrix code that provides increased accuracy.
2. Related Art
The “two dimensional bar code” was developed by NASA to identify and track space shuttle parts. The bar code pattern can be used to encode inventory data or a history of the object to which it is attached, as described in “A White Paper on Two Dimensional Symbols,” by Paul Mathans et al. (CSPI Vision Systems 1996).
The “two-dimensional bar code” is more formally referred to as a matrix code, a term that applies to two-dimensional codes that code data based on the position of dark modules within a matrix. All of the dark modules are the same dimension, and it is the positions of the modules that code the data. Data Matrix is a type of two-dimensional matrix code containing dark and light square data modules. It is designed to pack a lot of information in a very small space; a Data Matrix symbol can store between one and 3116 numeric or 2335 alphanumeric characters. A Data Matrix symbol has a finder pattern of two solid bars and two alternating dark and light square data modules on the perimeter of the symbol. These patterns are used to indicate both orientation and printing density of the symbol. A two-dimensional imaging device such as a CCD camera is used to scan the symbology.
The information in a Data Matrix symbol is encoded by absolute dot position rather than relative dot position. While a Data Matrix symbol is easily scalable between a 1-mil square to a 14-inch square, the actual limits are dependent on the fidelity of the marking device and the optics of the sensor. Data Matrix symbols can be used for small item marking applications using a wide variety of printing and marking technologies.
Additional information regarding Data Matrix code is disclosed in U.S. Pat. Nos. 4,939,354; 5,053,609; 5,124,536.
It is to the solution of these and other problems that the present invention is directed.